This paper describes the development of a brief school-based instrument designed for use in research and in educational practice. The "Survey of School Promotion of Emotional and Social Health" differentiates states of high, moderate, and low implementation of whole-school policies and practices that promote the emotional and social health of students. The instrument measures the extent to which a school has implemented policies and practices in four health-promoting domains: (a) creating a positive school community, (b) teaching social and emotional skills, (c) engaging the parent community, and (d) supporting students experiencing mental health difficulties. Responses were gathered via an online survey of Principals in almost 600 Australian primary schools in New South Wales. Preliminary psychometric properties of the instrument, and the development of an implementation index using latent class analysis, are described. The final 13-item version of the survey has broad applicability for use by researchers and evaluators for comparative and multivariate analyses. School leadership may find it useful as a brief tool to guide the identification of target areas for whole-school improvement across the four important health-promoting domains.